1. Field of Invention
The present invention relates to an actuator for use in a restriction apparatus, for example, to lift a vehicle hood or pull a steering wheel.
2. Description of Related Art
In addition to airbag-type restraining devices that are used in occupant restraining devices and pedestrian protecting devices for vehicles, there also are apparatuses that lift a vehicle hood in order to protect a pedestrian during collision and apparatuses that pull in (pull in toward the front end of the vehicle) a steering wheel in order to protect the vehicle occupant during collision.
These apparatuses use a pyrotechnic actuator and are known to be of a type in which a pin (piston) is pushed out and a type in which a protruding pin (piston) is pulled in by actuation.
In any case, an ignition device including an igniting agent, such as an igniter, is used and a combustion product such as high-temperature gas or shock wave generated therefrom hit the pin or piston directly, thereby driving the pin (or piston).
In such an actuator, a combustion product for driving a piston (that is, a source of piston-driving energy) can be retained better and higher efficiency can be obtained by disposing an actuation portion of an igniter, where an ignition agent is accommodated, in the vicinity of a piston head. However, the actuator structure does not always allow the actuation portion to be disposed close to the piston head, and loss of combustion products sometimes occurs due to a bent conveying path before the combustion products reach the piston head.
FIG. 1 and FIG. 2 of U.S. Pat. No. 3,261,261 disclose an actuator. A cylinder 18 is formed in a neck portion 17, and a piston 23 is disposed therein. A piston rod 25 is attached to the piston 23, and the piston extends to the outside from a port 26 of the body 13. A squib port 28 is formed in the neck portion 17, and a squib 29 having an explosive agent 30 that is in contact with a bridge wire 31 is disposed therein. The axis of squib 29 is disposed at a right angle to the axis of the piston 23. The distal end (portion where the explosive agent is disposed) of the squib is disposed at a certain distance from the piston head 23.
With such configuration, a space is present inside the squib port and a space is present inside the cylinder 18, and a combustion product generated from the explosive diffuses in these spaces, which causes loss of the combustion product. As a result, it may be that the force that pushes the cylinder head 23 is reduced.